Authentication page sometimes very long to load

pfsense 2 not yet in production but in a few days in replacement of monowall, i hope.
Everything is fine except authentication page of captive portal.
1: since i've enable https
2: no problem with certificate (comodo)
3: issue concern certains browser and versions of browser (IE:1 second to load / Firefox : 10s / Chromium: 10s / Epiphany : 40s).
4: not yet in production , so just 2/3 users connected. Pfsense is not overload.
5: in http mode, all browser take 1s to load the authentication page.
????
any idea.
is somebody concerning by the same issue ?